CTICasesPulmonary Artery Pseudo-Thrombus due to Bronchial Artery Inflow / Flow-Related Artifact
Imaging findings
A patient was referred with a presumptive diagnosis of pulmonary embolism, based on an outside PE study showing a filling defect in the left upper lobe pulmonary artery. However, this defect was only apparent on lung windows and not on standard soft tissue windows, with Hounsfield unit measurements consistently above 100-125 HU, highly suggestive of a flow-related artifact. The patient had underlying bronchiectasis and enlarged bronchial arteries in the region. A repeat, delayed CT scan confirmed no pulmonary embolism. This phenomenon can be attributed to heterogeneous contrast mixing and bronchial artery inflow.
Key takeaways
Flow-related artifacts can convincingly mimic pulmonary embolism on CT pulmonary angiography (CTPA), especially in areas of slow flow or where there is significant contribution from bronchial artery inflow, such as in patients with bronchiectasis. Careful windowing (comparing lung vs. soft tissue settings) and Hounsfield unit measurements are crucial for differentiating these artifacts from true thrombus. Anastomoses between bronchial and pulmonary arteries are known to occur in chronic inflammatory lung conditions, contributing to such mixing artifacts. Avoiding unnecessary anticoagulation in patients with underlying hemoptysis requires accurate differentiation.
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